1. Field of the Invention
This invention relates to lubricant compositions, and relates more particularly to lubricant compositions normally subject to oxidative degradation. The invention relates to lubricant compositions, such as oils of lubricating viscosity, hydrocracked lubricating oils, hydraulic oils, mineral oils or fractions thereof, automotive oils, gear oils, transmission fluids, waxes, greases and other forms of lubricants normally requiring the presence of stabilizing agents against oxidative degradation which may be catalyzed by ultra-violet light or the presence of metals, or which may occur during high temperature conditions.
2. Description of the Prior Art
In general, the production of lubricant compositions, for example, lubricating oils produced by hydrocracking affords a relatively high viscosity index and permits the use of certain stocks that would be unsuitable for other processes. On the other hand, however, hydrocracked lubricating oils tend toward poor stability against ultra-violet light degradation, rapidly forming suspended and/or precipitated insoluble material on exposure to ultra-violet light, such as sunlight, or other sources of actinic radiation. Compounds capable of absorbing ultra-violet light, for example, hydroxybenzophenones, and hydroxyphenyl benzotriazoles, have afforded some improvement in the light stability of hydrocracked oils. Conventional antioxidants have also provided some benefit.
In the literature, Heskins and Guillet in "Mechanism of Ultraviolet Stabilization of Polymers", Macromolecules 1, 97 (1968) first proposed the energy transfer mechanism of ultra-violet protection. Commercially available ultra-violet stabilizers are also listed by class and function and identified as to structure in the Kirk-Othmer Encyclopedia in "Encyclopedia of Chemical Technology"; Second Edition, Vol. 21, pp. 115-122. Uri in "Thermal and Photochemical Oxidation of Polymers and Its Prevention", Chemistry and Industry, Mar. 1, 1975, pp. 199-203, cites conventional antioxidant effects (hydroperoxide decomposition and free radical capture) of bis(stilbenedithiolato)nickel and its ultra-violet inhibiting properties. In British Patent Specification No. 1,263,910 (1972), there is disclosed bis(stilbenedithiolato)nickel as an antioxidant for plastic materials. The specification also cites superior hydroperoxide decomposition capability of this additive. U.S. Pat. No. 3,832,304, discloses the use of aromatic azo compounds for stabilizing hydrocracked oils. None of the foregoing disclosures show lubricant compositions containing the organo sulfur-containing nickel complexes described herein.